1. Field of Invention
This invention relates to A/D conversion, and more particularly to improved bipolar A/D conversion employing dual comparators with unipolar A/D conversion circuitry.
2. Description of the Prior Art
As is discussed more fully hereinafter with respect to the drawing, a common form of bipolar analog to digital (A/D) conversion circuitry employs selective polarity reversal at the input of a unipolar A/D conversion circuit. However, selective polarity reversal is achieved by means of a combination of an inverting video amplifier and a video switch ("video" simply meaning wideband analog), which selects between the uninverted analog input and the inverted analog provided at the output of the inverting amplifier. The video switch is very expensive and, in conjunction with the amplifier degrades performance due to slew rate (phase shift as a function of rates of change of input signals) and level offset, etc. Since the conversion can't begin until the polarity is tested, the switch is reversed and settled (as necessary), considerable time is lost, thus reducing the speed of conversion.